Tobacco in all forms - whether smoked or chewed first hand or second hand - may damage the heart, says a new study.

Koon K. Teo and colleagues at the University of Hamilton, Canada, studied data on more than 27,000 people in 52 countries for evidence that tobacco use affects heart attack risk.

Previous medical research has determined that smoking is a major contributing factor towards many health problems, particularly lung cancer, emphysema, and cardiovascular disease. Studies have also found that chewing of tobacco could cause oral cancer.

The study by Teo found that people who smoke, triple their risk of heart attack - and increase that risk by 5.6 per cent for every daily cigarette. Even light smokers who quit have a little extra risk of heart attacks three-five years after quitting, the researchers said.

Heavy smokers who quit see a rapid decrease in heart attack risk, but still have some extra risk even 20 years after quitting. Chewing tobacco more than doubles heart attack risk.

One to seven hours of second hand smoke exposure per week increases heart attack risk by 24 per cent, said the study. Further, over 21 hours a week of second hand smoke exposure ups heart attack risk by 62 per cent.

The study concluded that no level of tobacco use was found to be safe and second hand smoke may be more dangerous than previously thought of.